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Messages - Gm76

#1
Tech Help - Projects Page / biasing a Zygote
February 15, 2014, 04:33:16 PM
I am building a PNP germanium Zygote http://www.madbeanpedals.com/projects/Zygote/docs/Zygote.pdf with matched transistors from Smallbear and am using their suggested resistors in place of the trimpot.  In the Zygote instructions it says "You can sub in the values he indicates, if you like. If you still want to use the trim pot, adjust it so that the resistance on the pot + the 220R in series with it adds up to the value he indicates for the collector of Q2" I actually want to make it switchable between an external pot and the recommended fixed resistor value using a guitarpcb board.  Smallbear recommends 11K to bias Q2's collector.  My questions are  a) if the recommended value is 11K and I place a 11K resistor there, is the additional resistance by 220R negligible?  in other words, Do I need to place resistors in series to get as close to 10.78 as possible so that it adds up to 11K like it says in the instructions.  Seems like splitting hairs; B) if placing a resistor in place of the trimpot, I place it in the trimpot's 1&3 on the schematic, right?
Thanks
#2
Tech Help - Projects Page / Re: Cosmopolitan problem
January 22, 2014, 04:33:55 AM
I fixed it - the BC109 was bad, did not work in other circuits, don't know why i didn't test it at the same time as the germanium transistor.  I tried another BC109 and a BC108 and both worked fine - didn't hear much difference.  I still have to learn my way around a multimeter and audio probe and learn how to troubleshoot more comprehensively, but I'm glad I don't have to desolder board-mounted pots.
I guess what I was hearing before was the MOSFET stage, but I still don't understand: a) no sound w/ no transistor in Q2, but weak clean sound with the bad Bc109; b) weak clean sound with the germanium inserted CBE or EBC.
#3
Tech Help - Projects Page / Cosmopolitan problem
January 20, 2014, 05:31:51 AM
Finished populating a Haberdasher-etched board but when I hook it up to the breakout box I get a clean somewhat trebly sound less than unity despite maxing out all of the pots.  All of the pots seem to work, ie affect the tone or volume. If I pull the BS170, bc109, or germanium (not sure what, picked up from a forum member and is a little smudged,but has a green dot on the collector)  I do not get any sound.  I thought there might be a problem with the germanium transistor but when I subbed it into my boc npn fuzz face it worked fine.  Before that I thought I had Q3's collector and emitter mixed up but when I reversed them I got the same weak but clean sound - does that make sense?
I used a 220 pf ceramic cap in place of the 200 pf and used a 1n5818 in place of the 1n5817 diode based on what I had but was under the impression they wouldn't make a difference.
Unfortunately I used board-mounted pots so the back is pretty obscured, but I guess i can bend and/or remove pots to trouble shoot this. Any advice where to start? Thanks.
#4
Tech Help - Projects Page / Cosmopolitan cap choice
December 29, 2013, 08:53:58 PM
I see c2 calls for 200pf and I have 180 or 220 - are either of these acceptable subs? Thanks